Arsenal made a couple of late substitutions in this match, but that was no minor courtesy to the players introduced. It brought a welcome pause for the hosts as they held on to a 2-1 lead. A more luxurious moment came in stoppage time when the substitute Aaron Ramsey added a further goal with a very neat shot.

Arsène Wenger, serving a touchline ban, sat in the stands, leaving his assistant manager, Steve Bould, in charge. The latter saw a reaction to defeat by Chelsea last weekend. "It was tough, they made it tough for us. Without being fantastic," he said, "we got back on track before the weekend, which will be a tough game [at West Ham]."

There is something incongruous about thinking that a Champions League game could be some sort of warm-up for the Premier League. But, given their record, English clubs do have some cause to expect that a berth in the knockout phase is all but inevitable. Arsenal are more at ease in this competition than in domestic fixtures Victory was deserved here.

Olympiakos had shown endeavour but have now been beaten in both group games. Arsenal's concerns are marginal by comparison but they have failed to keep a clean sheet in any of their past six matches.

Arsenal's command, to put it kindly, fluctuated against Olympiakos. They took the lead in the 42nd minute with a low drive by the dynamic Gervinho from the edge of the penalty area after a tackle by Mikel Arteta had brought the opportunity. Just before the interval, Olympiakos equalised when Kostas Mitroglou got free of Laurent Koscielny to head home a delivery from Leandro.

Although there has been a partial overhaul of the team, Arsenal sometimes look as if the European scene is the setting in which they are more likely to flourish, even if Olympiakos did check them in the opening 45 minutes.

Thomas Vermaelen, the Arsenal captain, was disappointed by his side's performance before half-time. "The second half was better – in the first half we were sloppy sometimes with the passing, we lost a lot of balls," the centre-back said. "We started well but the first half was not great."

It is unlikely that Wenger could have altered this contest immediately if he had been allowed his place in the technical area. His judgment, all the same, was felt to a degree. In the alterations to the lineup following the defeat here by Chelsea, there was no place for the centre-half Per Mertesacker. Bould, though, explained that the player has been unwell.

No one should suppose Wenger is a detached intellectual rather than an intensely engaged manager. It must have been agonising when there were no instructions to be given. The Frenchman would have yearned to communicate when the visitors might have scored in the 35th minute. Paul Machado was in position to connect with a cross from José Holebas, but merely lifted it over the bar.

Arsenal were busy enough but Olympiakos, already beaten in the group by visiting Schalke, were ready to take the risk of committing men into attack. The hosts had to deal with that increased purpose if this occasion was not to introduce anxiety to Arsenal's expectation of a simple advance to the knockout stage.

There can have been few neutrals among the onlookers but this match could have been regarded as a pleasure by anyone who cared for excitement and unpredictability. The home supporters, however, took a more intense satisfaction as a more forceful side claimed a 2-1 lead.

There was a mixture of insistence and quality when Gervinho linked with Santi Cazorla before the latter's cross was blocked and the ball ran back for him to set up Lukas Podolski for a goal. The real trial for Arsenal, then, had been the spasmodic nature of their work. Compliments were due to Olympiakos for their commitment. Excuses could be made for the fact that Arsenal continue to be a work in progress after some recasting of the squad in a summer that included Robin van Persie leaving for Old Trafford.

Olympiakos would have reckoned that a consecutive loss in the group would be irreparable, but not many visiting teams would have challenged Arsenal with such vigour on this ground.

Wenger's men, at times, were still striving just to make sure that Olympiakos were kept at bay. Instead of calming a match that Arsenal must have expected to win with some ease, there was a need to marshall forces and protect the advantage.

On this night, negotiating the stretch of the path towards the last 16 was full of jeopardy and, indeed, fascination.